Conventionally, there are a large number of nitride semiconductor light-emitting elements such as LEDs (light-emitting diodes) or semiconductor lasers in which a light-emitting structure constituted by a plurality of nitride semiconductor layers is formed on a substrate such as sapphire by epitaxial growth (for example, see the following Non-Patent Documents 1 and 2). The nitride semiconductor layer is represented by the general formula Al1-x-yGaxInyN (0≤x≤1, 0≤y≤1, 0≤x+y≤1).
The light-emitting element structure has a double heterostructure in which an active layer is interposed between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer. The active layer is constituted by a nitride semiconductor layer having a single-quantum-well (SQW) structure or a multi-quantum-well (MQW) structure. When the active layer is an AlGaN based semiconductor layer, it is possible to regulate a band gap energy within a range, lower and upper limits of which are band gap energies that can be taken by GaN and AlN respectively (approximately 3.4 eV and approximately 6.2 eV) by adjusting an AlN molar fraction (also referred to as an Al composition ratio). Thus, it is possible to obtain an ultraviolet light-emitting element having an emission wavelength of approximately 200 nm to 365 nm. Specifically, as a forward current flows from the p-type nitride semiconductor layer to the n-type nitride semiconductor layer, light emission equivalent to the band gap energy occurs in the active layer.
Flip-chip mounting has been generally employed as a way of mounting a nitride semiconductor ultraviolet light-emitting element (for example, see FIG. 4 and the like in the following Patent Document 1). In the flip-chip mounting, light emission from an active layer is transmitted through an AlGaN based nitride semiconductor, a sapphire substrate, and the like having a larger band gap energy than the active layer to be extracted from the element. Consequently, in the flip-chip mounting, the sapphire substrate is faced upward, p- and n-electrode surfaces formed on the upper surface of a chip are faced downward, and the electrode surfaces on the chip are electrically and physically bonded via metal bumps formed on the electrode surfaces to electrode pads on a package component such as a sub mount.
In the flip-chip mounting disclosed in the following Patent Document 1, a nitride semiconductor ultraviolet light-emitting element in a bare chip state is mounted on a submount. Meanwhile, an LED illumination device, a liquid crystal backlight, and the like often employ a way of mounting light-emitting elements using a COB (chip on board) technique in which a plurality of bare chips are mounted on a submount or a wiring board and a plurality of light-emitting elements are connected in serial, parallel, or serial-parallel (combinations of serial and parallel connections) (for example, see the following Patent Documents 2 and 3).
In addition, in a printed wiring board for surface-mounting not only light-emitting elements but also electronic components, wiring patterns composed of a conductive material such as a metal are formed on an insulating board, and terminals or electrodes of surface-mounted components are physically or electrically connected to a part of the wiring pattern on which the electronic components or the like are surface-mounted (referred to as “pad”, “land”, or the like), so that the electronic components are surface-mounted on the printed wiring board. In general, a solder resist layer is formed on a surface of the board having the wiring patterns formed thereon for the purpose of preventing a short-circuit between the wiring patterns caused by a solder. A solder resist that is colored white is used for a submount or a wiring board for mounting a light-emitting element thereon, for the purpose of preventing the short-circuit described above and improving light emission characteristics (for example, see the following Patent Document 4).
Generally, as disclosed in FIGS. 4, 6, 7, and the like in the following Patent Document 5 or FIGS. 2, 4, 6, and the like in the following Patent document 6, the nitride semiconductor ultraviolet light-emitting element is practically used in a state of being sealed with an ultraviolet-transmitting resin such as a fluorine-based resin or a silicone resin. The sealing resin protects an ultraviolet light-emitting element within the resin from the outside atmosphere and prevents degradation of the light-emitting element caused by the entrance of water, oxidization, or the like. Moreover, the sealing resin is sometimes provided as a refractive-index reducing material that reduces the light reflection loss caused by the refractive index difference between a collecting lens and the ultraviolet light-emitting element or the refractive index difference between the ultraviolet irradiation space and the ultraviolet light-emitting element to improve light extraction efficiency. In addition, the surface of the sealing resin may be formed in a light-collecting curved surface such as a spherical surface, for the purpose of improving the irradiation efficiency.